Apparatus for attenuating voltage surges

ABSTRACT

In order to attenuate voltage surges which may occur on a highvoltage line upon closing or opening of a power switch located at an end of the line which serves to connect the line to a supply source, an attenuating resistance assembly which is structurally separate from the power switch itself is connected into the line on the line side of the power switch. This attenuating assembly includes a resistance component in series with the line and having connected in parallel with it a bypass switch and an overvoltage protective device which may be in the form of a spark gap. The bypass switch is opened prior to opening of the power switch, and the overvoltage protective device establishes a limit to the voltage which can be impressed across the attenuating resistance component. A compensating choke coil can also be connected to the line at either side of the attenuating resistance component. In a circuit closing operation, the power switch closes first followed by closing of the bypass switch after a brief time delay.

United States Patent 1,357,257 11/1920 Slepian APPARATUS FOR ATTENUATING VOLTAGE SURGES 4 Claims, 8 Drawing Figs.

U.S.Cl 317/11C, 200/144, 307/93, 317/16, 317/20 Int. Cl .l. H02h 7/22 Field of Search 307/93; 317/] l, 16, 20; 200/144 AP References Cited UNITED STATES PATENTS 2,802,149 8/1957 Germer et a1 317/11 FOREIGN PATENTS 999,802 2/1952 France 200/144 Primary Examiner lames D. Trammell Attorney- Pierce, Shceffler & Parker ABSTRACT: In order to attenuate voltage surges which may occur on a high-voltage line upon closing or opening of a power switch located at an end of the line which serves to connect the line to a supply source, an attenuating resistance assembly which is structurally separate from the power switch itself is connected into the line on the line side of the power switch. This attenuating assembly includes a resistance component in series with the line and having connected in parallel with it a bypass switch and an overvoltage protective device which may be in the form of a spark gap. The bypass switch is opened prior to opening of the power switch, and the overvoltage protective device establishes a limit to the voltage which can be impressed across the attenuating resistance component. A compensating choke coil can also be connected to the line at either side of the attenuating resistance component. In a circuit closing operation, the power switch closes first followed by closing of the bypass switch after a brief time delay.

PATENTEU JUN2 9 Ian SHEET 1 OF 3 Fig.2

Swan/Mom QUL BfLtlQngper j W2VPWAU APPARATUS FOR ATTENUATING VOLTAGE SURGES The present invention relates to apparatus to be connected in series with a power switch on'the line side at one end of a high-voltage line and which functions to attenuate voltage surges occurring on the high-voltage line during closing as well as opening of the power switch.

For the purpose of diminishing the voltage surges which occur during switching, it is known to provide power switches at the terminal point of the line with damping resistances connected in series with and, also in parallel with, the main power switch. This known arrangement involves the use of corresponding auxiliary switches for switching the damping resistances in and out. The resulting switch construction is complicated, which increases not only the cost but also the failure rate. In particular, the resistances must be dimensioned for the full switch pole voltage for switching in case of short circuit and of phase opposition. The same applies to the associated auxiliary switches. v

it is an object of this invention to provide a relative simple apparatus intended to be connected in series with a power switch on the line side at one end of a high-voltage line and intended to attenuate voltage surges occurring on the high-voltage line during closing and opening of the power switch.

According to the invention there is provided apparatus intended to be connected in series with a power switch but structurally separate therefrom at one end of a high-voltage line and intended to attenuate voltage surges occurring on the high-voltage line during closing and opening of the power switch, the apparatus comprising a resistance inserted in the line and there being connected in parallel therewith a bypass switch as well as an overvoltage protector.

Apparatus in accordance with this invention, being structurally separate from the power switch, is relatively simple to construct, with the additional advantage of a relatively small voltage load on the line inserted resistance. As is known, the ohmic value of the resistance should be about equal to the characteristic impedance of the line, i.e. several hundreds of ohms. An advantage of this apparatus is, that the power switch at the end or at the origin of the high-voltage line may be of simple construction because its damping resistance can be dispensed with, while the resistance and the bypass switch of the apparatus in-accordance with this invention can be more favorably dimensioned to a substantial extent.

Embodiments of the invention will now be described, by

way of example only, with reference to the accompanying schematic drawings wherein:

FIG. 1 is a schematic circuit diagram illustrating one embodiment of the invention wherein the attenuating resistance together with its parallel connected bypass switch and overvoltage protector are applied to a single-phase high-voltage line, the attenuating apparatus being connected in on the line side of a power switch located at one end of the line such as at a sub-station where power is fed into the line:

FIG. 2 is a schematic circuit diagram similar to Fig. l illustrating a modification wherein a compensating choke coil is incorporated to improve the desired attenuation effect during a switching out, i.e. an opening of the contacts of the power switch;

FIG. 3 is also a schematic circuit diagram similar to Fig. 2 but illustrating an alternative mode for connecting in the compensating choke coil;

FlGS. 4a and 4b are side elevations of two different forms of apparatus, each of which incorporates the circuit structure as shown in the Fig. l schematic;

FIG. 5 is a side elevation of a form of apparatus incorporating the circuit structure shown in the Fig. 2 schematic;

FIG. 6 is a side elevation of a form of apparatus incorporating the circuit structure shown in the Fig. 3 schematic, and

FIG. 7 is a schematic diagram illustrating one suitable arf rangement for effecting sequential operation of the power switch and bypass switch.

Referring first to Fig. l, a high-voltage line 1 can be connected and disconnected at its station-side end by means of a power switch 2. Reference numeral 3 designates a feeding voltage source to the line, e.g. one or more power stations. The power switch 2, contrary to practice prior to the present improved arrangement, has no damping resistance structurally associated with it however, between the switch 2 and the line 1 i.e. on the line side of the switch, there is connected an attenuating assembly 4 structurally separate from the power switch 2 in accordance with the invention which consists of a resistance 4a connected into the line, a bypass switch 4b connected in parallel with the resistance 4a, and an overvoltage protector 4c connected in parallel with the resistance 4a and also with the switch 4b. The overvoltage protector, in its simplestform, may, as illustrated, be constructed as a protective spark gap. The power switch 2 and the bypass switch 4b may be known types and are actuated in a sequence such that the resistance 40 becomes effective during the switching process over a predeterminable optimum period, e.g. 10 ms. The disconnection'sequence may, for example, be that the bypass switch 4b opens first and then, after a small lag, the switch 2 opens; the connection sequence may be that the switch 2 closes first and the bypass switch 4b then closes.

The attenuating assembly 4 shown in Fig. l is primarily intended to attenuate voltage surges during connection, but, depending on the ohmic value of the resistance 4a, also has a certain effect during disconnection. The protective spark gap 40 ensures that only a limited voltage will act on the resistance 4a. In the absence of the spark gap 40, the resistance 4a would have to be able to deal with the entire pole voltage, e.g. in the case of short'circuit or phaseopposition during connection. The bypass switch 4b may be constructed as a rapid-break switch having a certain power-switching capacity on connection and disconnection. Thus, for example, when connecting on short circuit it must be able to commutate, i.e. to take over and carry-the current of the spark gap 4c. if the high-voltage line 1 is equipped with compensating chokes, the latter may be expediently connected either as shown in Fig. 2 or as shown in Fig. 3. When the compensating choke 5 is connected as shown in Fig. 2, an especially advantageous attenuating effect will also be obtained during disconnection owing to the resistance 4a, because the resistance 4a, is included in the oscillatory circuit formed by the choke 5 and the line capacity.

FIGS. 4a and 4b both of which correspond to Fig. 1 show the main power switch 2 as a multiple type circuit-breaker in which a plurality. of individual power switch units are connected in series. in Fig. 4a the bypass switch 4b of the attenuating assembly 4 that is structurally separate from the power switch 2 is shown as having a single vertically disposed contact chamber, whereas in Fig. 4b the contacts of the bypass switch 4b are accommodated in a horizontally disposed double contact chamber. As already stated, Fig. 5 corresponds to Fig. 2, and Fig. 6 corresponds to Fig. 3. in all the Figures the same parts are denoted the same reference numerals.

Fig. 7 illustrates in a schematic manner one suitable arrangement for actuating the power switch 2 and the bypass switch 4b in their proper sequence. in this figure, 2a designates a relay contact or a control contact for initiating a closing operation of the power switch. 2b represents the closing coil for the power switch 2 and the appertaining trigger mechanism. This mechanism provides over a mechanical link 2c a mechanical impulse to the control mechanism 2e which, for example, may be constituted by a pneumatic piston. From this latter mechanism, the closing movement is transmitted to the contacts of the power switch 2 by one or a plurality of insulated rods 2f.

The closing coil and its trigger mechanism for the bypass switch 4b are designated by 4e and the contact closing mechanism by 4d. The desired time-delay in closing switch 4b following closure of switch 2 is obtained by controlling its closing coil 4e by means of an auxiliary contact 2d in the energizing circuit for this coil, the contact 2d being controlled by link 20 in the control for switch 2. Contact 2d closes a few milliseconds after closing of the contact 2a that serves to energize coil 2b. Regulation of this time-delay may be obtained in different manners, for example, by adding a mechanical timedelay device between and 2d. 7

To initiate an opening operation of the switches, the mechanism depicted operates according to the same principle but in reverse so that the bypass switch opens first followed by opening of the power switch 2 after a brief time-delay.

The drawings illustrate the apparatus 4 only for single phase and on only at one end of the high-voltage line. It is obvious that the apparatus 4 may be constructed for multiphase operation, and may be provided at both ends of the high-voltage line.

I claim:

1. An arrangement for switching longhigh-voltage alternating current transmission lines comprising a power switch located at one end of the transmission line, and an attenuating assembly for attenuating voltage surges which occur as a result of actuating said power switch, said attenuating assembly being structurally separate from said power switch and including an attenuating resistance connected in series with said transmission line on the line side of said power switch, a bypass switch connected in parallel with said attenuating resistance, and an overvoltage protective device also connected in parallel with said attenuating resistance.

2. Apparatus as defined in claim 1 wherein said overvoltage protective device is constituted by a spark gap.

3. Apparatus as defined in claim 1 and which further includes a compensating choke connected between said line and ground at a point on said line intermediate said power switch and said resistance component.

4. Apparatus as defined in claim 1 and which further includes a compensating choke connected between said line and ground at the line side of said resistance component. 

1. An arrangement for switching long high-voltage alternating current transmission lines comprising a power switch located at one end of the transmission line, and an attenuating assembly for attenuating voltage surges which occur as a result of actuating said power switch, said attenuating assembly being structurally separate from said power switch and including an attenuating resistance connected in series with said transmission line on the line side of said power switch, a bypass switch connected in parallel with said attenuating resistance, and an overvoltage protective device also connected in parallel with said attenuating resistance.
 2. Apparatus as defined in claim 1 wherein said overvoltage protective device is constituted by a spark gap.
 3. Apparatus as defined in claim 1 and which further includes a compensating choke connected between said line and ground at a point on said line intermediate said power switch and said resistance component.
 4. Apparatus as defined in claiM 1 and which further includes a compensating choke connected between said line and ground at the line side of said resistance component. 